I didn't know the existence of the accumulate function in C. Glad to have read your post. IO don't have much time this week to dig into the code, but you can probably inspire yourself from those have solved the exercises already to double check what is going on. I will stay available for the extra questions.

To answer the few questions:

• JetCleaning is not related with photons, but with leptons (to remove electrons from the jet collection that can potentially be considered as jets when not specifically identified as electrons).
• by default, particles are ordered decreasingly in terms of pt. but this can be changed thanks to the SORTER service.

For the future, I'd like to be able to fabricate datasets to test code. I'm hoping this will come up during the verification phase.

This is phase 2. Once I will have beta versions for the analysis I am proposing in the TRs, we will get there. Do you plan to try these out? :)
I am also happy to see one extra participant to this project.